@asdofindia/markdown-it-table-of-contents
This is a fork of Oktavilla's markdown-it-table-of-contents that changes the default header levels included to [1, 2, 3, 4].
That's all it does.
(I had to do this because I couldn't set options in pug's template that uses jstransformer-markdown-it which calls markdown-it without setting options)